Washington failed to take advantage of an opportunity to clinch a first-round series victory in Game 6 on Sunday at Verizon Center, falling, 4-3, to the Bruins in overtime. With Tyler Seguin’s game-winning goal 3 minutes 17 seconds into the extra session, Boston evened the series at three games apiece and forced a winner-take-all Game 7 on Wednesday at TD Garden.

It’s been an uncannily close series, with six straight games determined by a one-goal margin for the first time in NHL history, so perhaps it’s fitting that it will require one more gut-wrenching contest. But while the Capitals certainly would have preferred to end things at home rather than give Boston another chance at life, no one expected the defending Stanley Cup champions to roll over.

“They’re not gonna die easy,” forward Matt Hendricks said. “They came out hard. You could tell right from the first period that they were ready to play tonight. It was do or die for them, so they came out hard.”

Like every game before it in this matchup, Game 6 offered more tight, back-and-forth action. Washington fought back to erase three one-goal deficits over the course of regulation, but in overtime it was the Bruins who came out flowing and anxious to ensure their season would be extended three more days.

After two quality scoring chances in the extra session, the Bruins capitalized on an uncharacteristic turnover by Nicklas Backstrom. Washington’s top centerman tried to force a pass through the neutral zone that was picked off by David Krejci, sending the Bruins’ rush back into the offensive zone.

Milan Lucic passed the puck to Seguin, who displayed incredible patience to wait out Capitals netminder Braden Holtby so he could shoot into an open net for the game-winner.

It was a shot the 22-year-old rookie said he would have liked to have back, and a turnover the veteran centerman knew he could have prevented.

“That’s a save that I want to make and I should have learned from the play before that,” said Holtby, who finished with 27 saves. “That they were going to try and out-wait like that if they had time. It was my fault.”

Said Backstrom: “I was trying to hit Marcus [Johansson] there but I missed the pass, so bad turnover by me. We’ve got new chance on Wednesday, just got to refocus and make sure we play our best game.”

Before overtime it appeared as though the Capitals might have had the momentum to close out the series in dramatic fashion in front of their raucous, red-rocking supporters. While Boston took the lead three times in the game, including one at 3-2, 11:57 into the third when Andrew Ference scored on a rebound, the Capitals worked their way back each time.

Captain Alex Ovechkin recorded his second goal of the series with 4:52 remaining in regulation. The goal came off of a Backstrom faceoff win against Rich Peverley, who was taking draws instead of Patrice Bergeron because of an upper-body injury that prevented Boston’s top centerman from taking his place at the center of the circle most of the night.

As Ovechkin slammed himself into the glass to be mobbed by his teammates and Verizon Center erupted, the energy for the home team likely couldn’t have been higher. But Boston relied on its experience of playing in the face of elimination — the Bruins faced four elimination games on their Stanley Cup run in 2011 — and refused to wilt.

“You expect your team to show again the experience that they’ve gained in the past. I said that tonight before the game, before Game 6,” Bruins Coach Claude Julien said. “When you go through those kinds of situations, you can handle those a lot better.”

Boston struck first in the second of back-to-back matinee contests, ending a string of four straight games that saw the Capitals take the initial lead. Peverley put the Bruins ahead 1-0 5:56 into the first period when he tipped a point shot in the high slot past Holtby. Mike Green tied the score at 1 less than four minutes later,with a shot that went off of Boston defenseman Greg Zanon, for his first goal since Oct. 22.

Krejci scored a power-play goal with 16:48 gone in the first to give Boston a 2-1 lead and the first advantage it carried into the second period all series. Then it was Jason Chimera’s turn to stabilize the contest for Washington when he knocked home a back-door feed by Backstrom with 41.9 seconds left in the middle frame.

Boston and Washington exchanged tallies once more in the third — goals by Ference and Ovechkin. After rallying to even the score three separate times in each period of regulation, the Capitals were disappointed they couldn’t find a way to wrap things up in overtime.

“The losses like that are deflating. It’s tough,” defenseman Karl Alzner said. “But you never would have thought that we’d win the series against Boston in six games. You’d think it’d go to the end, anyways. We weren’t getting too far ahead of ourselves. We knew that it was going to be tough.”